The present invention relates to degassing apparatus used in the fabrication of metals such as aluminum, copper and steel and more particularly to such a device that may serve the dual function of metal degassing and additive addition in alloying or other furnace operations.
In the fabrication of metals such as aluminum, copper and steel (hereinafter xe2x80x9cmetalxe2x80x9d), an important part of the operation of converting the metal from a molten state to a solid and further fabricable state is the removal of gases such as hydrogen that may result in porosity or xe2x80x9cvoidsxe2x80x9d in the solid state metal. Such xe2x80x9cvoidsxe2x80x9d can result in areas within the volume of the solid metal that exhibit properties different, normally weaker, than those of the surrounding metal and give rise to the presence of stress risers that can provide initiation points for propagation of cracks or other defects in the finally fabricated metal. Accordingly, a great deal of effort in the metal refining operation is dedicated to the removal of hydrogen and similar elements that can result in a finished product that does not meet product specification properties. Such metal treatment processes are conventionally referred to as xe2x80x9cfluxingxe2x80x9d and is generally performed through the exposure of the molten metal to a gas or mixture of gases such as argon, chlorine, CO2, CO, etc.
It is also conventional practice in such metal fabrication furnace operations to add grain refiners, alloying elements, etc. to modify/improve the properties of the metal undergoing treatment.
In fabrication operations equipped with large furnaces, e.g. 20 to 50 tons in, for example, the aluminum industry, fluxing is performed in any number of different ways using a variety of equipment. Some more recently constructed metal melting and/or holding furnaces or metal retention vessels or crucibles are equipped with porous plugs in their bottoms. A xe2x80x9cfluxingxe2x80x9d gas such as chlorine, argon or mixtures of same are introduced through the porous plugs and permitted to move upward through the metal contained in the furnace scavenging hydrogen as it rises. In older furnaces, not equipped with porous plugs, cylindrical xe2x80x9cwandsxe2x80x9d or turrieres through which xe2x80x9cfluxingxe2x80x9d gas is introduced are manually or mechanically circulated within the body of molten metal to provide the fluxing gas to the lower portion of the molten metal body. As the gas rises it scavenges the potentially damaging hydrogen gas contained in the body of the molten metal. While the porous plug approach can be designed and implemented to provide substantially 100% treatment of the metal contained in the furnace, the affect of fluxing with wands can be variable depending upon the experience and dedication of the operator, retention time in the furnace and the design of the head or gas dispersing device attached to the end of the wand.
xe2x80x9cFluxingxe2x80x9d in smaller installations is often more problematic. In such installations, for example those associated with smaller casting operations in aluminum extrusion plants and foundry casting operations, where molten metal furnaces and retention device capacities may be measured in pounds rather than tons, fluxing is often performed using wands as described above. Again, such operations offer the opportunity for under fluxing.
One device proposed to improve the fluxing operation is described in U.S. Pat. No. 3,972,709 issued Aug. 3, 1976. The device of this patent comprises a supply conduit connected at one end to a source of pressurized gas and connected at the other end with a rotatable closed cylinder, i.e. one having a cylindrical wall, a top and a bottom, immersed in the molten metal. An array of apertures extends through the wall of the cylinder for discharging the gas into the molten metal. The apertures are arranged to discharge the gas in the form of numerous gas bubble jets in mutually cooperative jetting directions to rotationally propel the cylinder about the supply conduit. Physical contact between the molten metal and the gas within the cylinder is prevented by adequate flow of the gas through the apertures.
The addition of grain refiners and the like in such molten metal furnace operations is also accomplished in a variety of ways. In some cases solid additives are simply xe2x80x9cdumpedxe2x80x9d or plunged into the furnace, a practice that can result in the loss of significant quantities of the additive and a lack of proper dissemination of the additive throughout the body of molten metal thus often providing a somewhat less than homogenous molten metal body. In other cases the additive(s) are injected under the molten metal surface, a practice that generally requires the use of an additional costly piece of equipment and the purchase of additives in a very specific size and formulation that must be purchased from the supplier of the injection equipment, generally at a higher cost.
Thus, there exist a number of more or less reliable methods for the individual introduction of fluxing gases and additives into molten metal in furnace operations. There does not however, to the best of my knowledge exist a device that while enhancing the dissemination of fluxing gas in fixed or movable wanding operation also offers the potential for the simultaneous introduction of additives to provide a uniform or homogeneous metal melt.
Thus, the availability of an efficient, relatively inexpensive and simple to utilize combined fluxing gas/additive introduction device or system suitable for use in molten metal handling operations would be of significant value to the metal processor. Such a device would enhance the reduction of hydrogen in processed metal while offering the potential to simultaneously improve the dissemination/dispersion of additives in such molten at a reduced cost and with simple operating procedures.
It is therefore an object of the present invention to provide and improved head for molten metal fluxing devices that enhances the dispersion of fluxing gas in molten metal when a moveable of fixed wanding technique is used to introduce the fluxing gas to the molten metal.
It is another object of the present invention to provide an improved flux gas introduction device for the head of a fluxing wand that also offers the potential for the simultaneous performance of fluxing operations and the introduction of grain refiners and other metal additives in a manner that improves the dispersion/dissemination of such additives into the molten metal.
A tool or fluxing head for fluxing molten metal that comprises a fluxing gas supply line that communicates with the interior of an inverted cup providing a hollow center into which refining agents and other additives that are to be introduced into a molten metal can be incorporated. In use, the fluxing head is introduced into a molten metal body with the cup in the inverted position. The inverted cup has a closed top at the point where the gas supply line enters and an open bottom that allows molten metal to enter the inverted cup to make contact with the refining agent or other additive. Apertures are provided in the side(s) of the inverted cup to allow gas introduced therein to escape therefrom. According to a preferred embodiment, a porous medium is provided at the top of the inverted cup to allow for the escape of gas into the molten metal through the porous medium.